The present invention is directed to control devices for bicycles and, more particularly, to a twist-grip shift control device for shifting a bicycle transmission.
An example of a twist-grip shift control device is shown in U.S. Pat. No. 5,921,139. That shift control device comprises a fixed member that is nonrotatably fixed to the bicycle handlebar, a handgrip operating member rotatably supported relative to the fixed member for rotating in first and second directions, a takeup member rotatably mounted relative to the fixed member for controlling the pulling and releasing of a transmission control element, and an intermediate member coupled for rotation with the takeup member. Ratchet teeth are formed on the fixed member and the intermediate member for holding the intermediate member, and hence the takeup member, in a plurality of fixed positions. Additional ratchet teeth are formed on the intermediate member and the handgrip operating member for rotating the intermediate member and the takeup member for pulling and releasing the transmission control element. A pulley is mounted to a bracket that extends from the base member for changing the direction of the transmission control element after the transmission control element exits the takeup member so that the transmission control element can extend in the direction of the bicycle handlebar.
It was learned that the tension on the transmission control element affects the operation of the shift control device. More specifically, the amount of the transmission control element pulled or released between the fixed positions of the takeup member would vary depending upon the tension applied to the transmission control element, thus causing the transmission attached to the transmission control element to be placed in a position that was not optimum for the selected gear. Such positioning errors could cause the transmission to generate undesirable noise or to malfunction.
The present invention is directed to a twist-grip shift control device that operates reliably even when the transmission control element experiences high tension. In one embodiment of the present invention, a bicycle shift control device comprises a base member for attachment to the bicycle, a operating member rotatably supported relative to the base member for rotating in first and second directions, a transmission control member rotatably mounted relative to the base member for controlling the pulling and releasing of a transmission control element, a bracket for supporting a transmission control element diverting surface, and an intermediate member coupled for rotation with the transmission control member. The intermediate member rotates around a first axis, and the intermediate member can move in the direction of the first axis between an engagement position, in which the intermediate member engages the bracket, and a disengagement position, in which the intermediate member is disengaged from the bracket. More specifically, the intermediate member includes a first cam surface for causing movement of the intermediate member in the direction of the first axis toward the disengagement position during rotation of the intermediate member, and the intermediate member includes a positioning surface for preventing the intermediate member from rotating around the first axis when the intermediate member is in the engagement position. Having the intermediate member engage the bracket in the engagement position minimizes or eliminates variations in performance caused by tension exerted on the transmission control element.